1. Field of the Invention
The present invention relates to an image forming apparatus; specifically relates to an image forming apparatus such as a copying machine and a printer device using an electrophotographic system or an inkjet system; and more particularly relates to an image forming apparatus that can respond to interrupt processing when the number of signal lines is reduced.
2. Description of the Related Art
A copying apparatus with an electronic photographic system has various types of units that can be freely interchanged by attaching and detaching to the main body of the apparatus, and is driven and controlled by image forming control means having a CPU in the main body of the image forming apparatus. Signals indicating the attachment/detachment status of these various kinds of interchangeable units with the main body of the apparatus are input to the image forming control means as input signals from detection means provided in each unit.
In recent years, with the development of color, high performance and multi-capability image forming apparatuses, there has been a tendency to increase the number of signal lines for the input signals from the various types of detection means and for the output signals to the actuators. Moreover, to use the various types of detection means and actuators, a power supply other than the detection results signals and the drive signals is necessary. In order for the image forming control means to input and output detection signals from the these numerous detection means and drive signals to the drive means, numerous signal lines and power source lines are necessary, and the image forming control means becomes large. Moreover, the image forming control means is set up in a location separated from the various units and detection means, and therefore numerous signal lines wind around inside the apparatus, which is a great impediment to making a simplified, small-scale and low cost apparatus.
In order to prevent the proliferation of signal lines in this way, image forming apparatuses such as that indicated, for example, in Japanese Unexamined Patent Application No. 2002-258691 (Prior Art 1) provide an I/O expander in each unit, and the number of image forming control means and unit connection signal lines are reduced by the image forming control means identifying the kinds of units from the status of the input port of the I/O expander.
Moreover, image forming apparatuses such as that indicated in Japanese Unexamined Patent Application No. 2006-218682 (Prior Art 2) are set up with the transfer clock at the L level, the transfer data acquired when the transfer clock starts up is taken as image serial data, and the image serial data and the control signals are transferred using a common data signal line by taking the data transfer start up signal when the transfer clock is at the H level as the control signal.
When the image forming control means forms an image, it is necessary to carefully control the drive means and actuators corresponding to the operational status inside the apparatus and to the status at a plurality of locations in the apparatus. In order to carefully control the drive means and actuators in this way, by identifying the types of units from the status of the input port of the I/O expander of the various units as indicated in Prior Art 1, the number of image forming control means and of unit connection signal lines becomes smaller, and even if the image serial data and control signals are transferred by common data signal lines as indicated in Prior Art 2, the number of signal lines for input to the image forming control means and the number of signal lines for output is enormous, and the apparatus becomes complicated and difficult to make compact.
Thus, by using an I/O control method that places signals from a plurality of status detection means (sensors) or drive control signals to a plurality of drive means on one shared signal line, the enormous number of data input/output lines of the image forming apparatus is reduced, and at the same time, versatility is maintained such that accommodation can be made without increasing the number of signal lines even if the image forming system configuration is modified by increasing or decreasing the number of detection means or actuators. Here, because the I/O means data is necessarily transacted from the main controller, the I/O control method uses extensive interrupt processing and is not adapted for acquiring irregularly generated signals.